If "use rich text editing" has been enabled (Administration > System > System Settings > System Defaults), special formatting and embedded images or links can be added using the Rich Text Editor menu that appears directly above the article's contents when adding or editing an article.
If "use rich text editing" has not been enabled, special formatting and embedded images or links can be added using HTML tags. Clicking on the "adding links or special formatting to your article..." link will take you to a separate window which will help you format links and upload images. This window also provides instruction on adding special formatting to your text.